Twisted Bodipy Derivative as a Heavy-Atom-Free Triplet Photosensitizer Showing Strong Absorption of Yellow Light, Intersystem Crossing, and a High-Energy Long-Lived Triplet State

A Bodipy derivative with twisted π-conjugation system is demonstrated that shows efficient intersystem crossing (ISC) (singlet oxygen quantum yield ΦΔ = 55%) and a long-lived triplet state (τT = 197.5 μs) with high energy (ET1 = 1.44–1.53 eV). This is superior to the conventional heavy-atom-enhanced ISC in a reference Bodipy compound, which results in much shorter triplet state lifetime (3.3 μs) and lower triplet-state energy (1.2 eV).